Patellofemoral (PF) pain, also called patellofemoral syndrome, is recognized as the most common musculoskeletal condition involving the knee and the number one musculoskeletal diagnosis among adults between the ages of 25 and 40 years who participate in recreational sports. In terms of relevance to the VA population, there are currently 2.6M veterans between the ages of 25 and 40 who are at risk if they participate in recreational sports. Many cases of PF pain in veterans may be service connected. In a group of veterans of the first Gulf War, 13% were diagnosed with PF pain and in a separate study of infantry soldiers, patellofemoral syndrome was the number one cause of disability claims. The prevalence of PF pain in military personnel is relevant to the VA because of the known chronicity of PF pain. Nearly 75% of patients diagnosed with PF pain still experience pain five years following initial presentation and 25% of patients with PF pain have symptoms that persist for up to 20 years. Thus, a substantial proportion of military personnel who develop PF pain during active service will continue to have symptoms as those individuals transition to veteran status. The cost of treating veterans with PF pain is dramatic. Based on newly available prevalence and cost data, we estimate that the medical costs associated with the treatment of PF pain in veterans in just the first year following diagnosis is $1.5B. By comparison, the medical cost for treating Iran and Afghanistan veterans is currently estimated to be $2.0B per year. In an editorial on patellofemoral pain, one clinician noted that treatment is often based on traditional beliefs regarding patellofemoral biomechanics and all too often, the clinical results from this type of approach are less than desirable. As a possible justification for the use of traditional beliefs rather than solid evidence-based medicine, one prominent research group stated the aetiology, pathogenesis, and recommended treatment [of PF pain] remain unclear. These statements are as true today as they were a decade ago. In recent years there has been an evolving awareness that quantifying the tissue stresses within the PF joint may provide new insight into one potential cause of PF pain. A critical barrier to testing this stress hypothesis is an absence of well-designed studies in which stresses within the PF joint are compared between groups of subjects with PF pain and healthy, age and gender-matched pain-free controls. In turn, a significant obstacle to performing well-designed studies is a lack of knowledge of the means and the standard deviations, of the tissue stresses for the respective groups of subjects. Without having a good estimate of the variation in tissue stress across a relevant population it is impossible to design a robust study based on hypothesis- specific power calculations. Since tissue stresses cannot be directly measured in vivo, computational analysis must be used to calculate stress using anatomical and physiological-based models. Over the past seven years, our research team has accumulated a comprehensive data set on a large cohort of PF pain subjects. To date we have acquired advanced imaging data during upright weight-bearing, along with motion capture data and EMG data for fifty subjects with PF pain and for fifteen healthy controls. These data have been de-identified and are available for further processing. We have also developed a modeling pipeline to facilitate the creation of high- fidelity finite element models from imaging and muscle activity data. The goals of the proposed pilot study are: 1) to eliminate a critical barrier to progress by determining the means and standard deviations of the tissue stresses in the PF joint in subjects with and without PF pain; and 2) to determine the sensitivity of the tissue stresses to uncertainties in model input parameters. The results of our proposed pilot study will enable the robust design of future studies that focus on the role of tissue stresses as a potential cause of PF pain and on novel interventions that might alter tissue stresses and alleviate pain.